I don't really understand why one would build an HTTP API for this. I can't imagine the database being more than a few megabytes, the whole thing could probably be served as a JSON file.
I assume it's intended to be used in an educational context. Learning how to work with a simple API is more fun that way.
The last category on the left sidebar is "FHGR", which I'm guessing stands for Fachhochschule Graubünden, and indeed under IM2 we find:
> APIs handpicked by the University of Applied Sciences of Grisons for their IM2 JavaScript programming course...